Follow-up widening the archived-history fix to the sibling save paths the
original PR did not cover. Model switches (_cmd_model, set_session_model) and
_restore mint a fresh AIAgent with _session_db_created=False, so the
agent-owns-persistence guard evaluates False and the blind full-history
replace_messages() fired — DELETEing the durable active=0/compacted=1 rows on
any compressed ACP session (same data-loss class the PR fixes, different
trigger).
- hermes_state.replace_messages: add active_only=True to delete/reinsert only
the live (active=1) rows, leaving soft-archived rows untouched (idea adopted
from the competing PR #50306 by @mrparker0980, credited).
- hermes_state.has_archived_messages: cheap existence probe for active=0 rows.
- acp_adapter._persist: when the agent doesn't own persistence but the session
already has archived rows on disk, replace active-only; otherwise the
destructive full replace stays (fresh create/fork has nothing to lose).
- Regression test: model-switch save on a compacted session keeps the archived
turn discoverable via get_messages(include_inactive=True) + search_messages.
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